I attended this year's Atea Community in Ålesund, which as usually starts off with something about team work and motivation mixed with soccer. This year was no exception, and one of the things mentioned was that if a person is convicted for drug use, they will be blocked from ever entering the USA.
If we look away from the fact that this is a fear-induced lesson rather than a motivation (as long as you stay off drugs, you are welcome to visit the USA), I started to think of the legal implications. Drugs by whose definition?
You could be convicted for the consumption of alcohol in a country where this is considered a drug. Consumption of alcohol is legal in the USA. Being blocked could be a recognition that you did not heed the law of the country you were convicted in.
On the same note, you can drink alcohol when you're 18 in Norway, which means you have practically broken the law in the USA, where you must be 21. Or you have been smoking marijuana in the Netherlands, which is banned in most US states. This could be taken as evidence that you don't respect the laws in the US, since you have already engaged in activities that go against those laws.
Drug legislation is not unique. US legislation claims jurisdiction on all US citizens, no matter where they are in the world, which means that a person easily could end up in a legally impossible situation, where doing something would break US laws and not doing it would break local law.
It would be wise to just keep jurisdiction geographic before people suddenly find themselves with a state sanctioned citizenship of a different country against their will.